Vehicles may be fitted with fuel vapor recovery systems wherein vaporized hydrocarbons (HCs) released from a fuel tank (for example, during refueling) are captured and stored in a fuel vapor canister packed with an adsorbent, such as activated charcoal or carbon. At a later time, when the engine is in operation, the fuel vapor recovery system may use a vacuum (or pressure) to purge the vapors into the engine intake manifold for use as fuel. The purge flow vacuum (or pressure) may be generated by one or more pumps and/or ejectors or by pressures in the engine intake manifold.
The inventors herein have recognized that with increasingly stringent engine emission standards and reductions in engine manifold vacuums to increase fuel economy it may be desirable to design an evaporative emissions canister that is efficiently cleaned through what little purge air is available. For example, reductions in engine manifold vacuum may reduce an amount of vacuum available to adequately purge fuel vapor stored in a fuel vapor canister resulting in increased emissions. Further, approaches which utilize a pump to provide vacuum to a fuel vapor canister for purging may reduce fuel economy due to parasitic power consumption by the pump.
In order to address these issues, in one example approach, a method for an engine with a fuel vapor recovery system including a multi-tubular fuel vapor canister is provided. The method comprises directing air through a first set of adsorbent passages in the fuel vapor canister to purge fuel vapor therefrom while not directing air through a second set of adsorbent passages in the fuel vapor canister; and directing air through the second set of adsorbent passages to purge fuel vapor therefrom while not directing air through the first set of adsorbent passages. In another example, a method includes flowing purge air through different groups of parallel-tubular fuel vapor canister passages depending on operating conditions.
Such approaches utilize a purge efficient/cost efficient evaporative carbon canister which may be more thoroughly purged with a reduced amount of purge vacuum thus reducing evaporative emissions while increasing engine fuel economy.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.